The present invention relates to a method for improving the mold releasability of a polymeric material such as thermosetting and thermoplastic resins and rubbers. More particularly, the invetion relates to a method for improving the mold releasability of a polymeric material by admixing the polymeric material to be molded with a specific organosilicon compound as an internal mold release agent.
It is conventional in the molding process of a polymeric material including thermosetting and thermoplastic resins such as vinyl chloride resins, acrylic resins, epoxy resins, urethane resins and the like and rubbers such as natural rubber and various kinds of synthetic rubbers to coat the inner walls of the metal mold with a mold release agent by spraying or brushing with an object to facilitate releasing of the molded polymeric body from the metal mold. The mold release agents currently used in the above mentioned purpose are mostly prepared on the base of a petroleum wax, a silicone or a combination thereof. The method of coating of the metal mold with a mold release agent has several problems. For example, the effect obtained by the coating is not lasting so that the inner walls of a metal mold must be coated frequently when the metal mold is used repeatedly so that the productivity of the molding process cannot be high enough due to the interruption of the molding process for coating of the metal mold with a mold release agent. Further, the metal mold is unavoidably stained by the accumulation of the decomposed mold release agent so that the metal mold must be cleaned periodically taking a great deal of time and labor. The mold release agent scattered in the spray coating of the metal mold may cause envionmental contamination. In addition, the surface of the shaped body molded in a metal mold coated with a mold release agent not always can be satisfactory in respect of the luster and feeling in touch though dependent on the types of the mold release agent and the amount thereof deposited on the surface of the shaped body.
Alternatively, it is also proposed to facilitate mold releasing of a polymeric shaped body from a metal mold by admixing the polymeric material before molding with a mold release agent, which is called an internal mold release agent. Use of such an internal mold release agent is also not free from several problems. For example, certain internal mold release agents contain various functional groups in the molecular structure so that the resins and rubbers admixed therewith may be reacted with the functional groups so that various adverse effects are caused on the properties of the shaped polymeric bodies. In particular, difficult problems are involved in the use of an organopolysiloxane-based internal mold release agent admixed with polyurethane foams because the foams are sometimes destroyed or the uniformity of the cellular foam structure is decreased.